The Michaelson Interferometer was invented in the late 1800's, and since has been widely adopted across many disciplines to create spectra from an incoming light source. Fourier Transform Interferometer based systems are used in research for assay determination, for chemical composition of samples such as for the pharmaceutical industry, on factory floors for monitoring effluent and/or air quality, etc. One application where interferometers have found particular success is in use related to detection of the infrared region of the electromagnetic spectrum. In such a role, Fourier Transform Interferometer Infra-Red (FTIR) systems may, for example, be used to measure trace gases in the earth's atmosphere.
Atmospheric measurement systems are however often employed on aircraft, and thus exposed to high levels of vibration. A fundamental design difficulty for maintaining interferometer accuracy stems from the need to maintain optical alignment of two opposing mirrors as they are physically moved when increasing the optical path difference (OPD) between them. To ensure that an interferometer remains reliable, it must be substantially immune to environmental vibrations, but this is an extremely difficult task in aircraft applications.
Typically, interferometers have a number of reflecting mirrors and two opposing retroreflectors. Generally, one of the reflecting mirrors is mounted movably in a longitudinal direction, i.e. along the path of the radiation beam, while the other is fixed. When constructing the arrangement for the movement or longitudinal displacement of the movable mirror (or reflector), effort must be made to ensure accurate displacement. Between these two mirrors is a third optical component called a beamsplitter. Attaching both mirrors to a single frame that moves relative to the beamsplitter has led to FTS systems has been introduced as a potential alignment fix, but this creates an instrument having a limited maximum optical path and/or introduces shear in the optical alignment.
The embodiments described below overcome these and other problems and an advance in the art is achieved. The embodiments described below provide an interferometer design that joins the two required mirrors in a single mechanism—a translation mirror mount that moves relative to the base housing the beamsplitter. The design of the present embodiments has no OPD limitation due to mechanical design induced shear, so an arbitrarily large OPD could be realized. Furthermore, optical misalignment introduced by a relative tilt between the base and translation mirror mount is largely self-correcting.